The present invention relates generally to weldable nickel aluminide alloys, and more particularly to such nickel aluminide alloys and weld filler metal formed therefrom containing concentrations of zirconium greater than in previously available nickel aluminide alloys for significantly increasing the resistance of the present nickel aluminide alloys and previously known nickel aluminides welded by the present filler metal to weld hot cracking during the welding thereof.
Recently developed nickel aluminide alloys possess various properties such as desirable high temperature yield strength and ductility, high resistance to oxidation, and room temperature yield strengths greater than 80 ksi in an "as cast" condition. These properties make these alloys particularly suitable as engineering materials for use in many structural applications and product forms including sheet, plate, bar, tubing piping, wire, and castings. Nickel aluminide alloys possessing these properties are described in assignee's U.S. Pat. No. 4,731,221, issued Mar. 15, 1988 and entitled "Nickel Aluminides and Nickel-Iron Aluminides For Use In Oxidizing Environments" and in assignees's U.S. Pat. No. 5,108,700, issued Apr. 28, 1992 and entitled "Castable Nickel Aluminide Alloys For Structural Applications".
While the nickel aluminide alloys such as described in these patents represent significant improvements over previously known nickel aluminide alloys, these alloys have been found to have poor resistance to weld hot cracking so as to cause these alloys to be classified as being of poor weldability as evidenced by the high level of difficulty in providing and reproducing crack-free welds. For example, the nickel aluminide alloys identified in assignee's aforementioned patents as IC221 and IC396 and respectively having a composition of a nickel base with, in wt. %, 8% aluminum, 7.7% chromium, 1.5% zirconium, and 0.003% boron, and a composition of nickel base with 8% aluminum, 7.7% chromium, 3% molybdenum, 0.85% zirconium, and 0.003% boron have been welded by gas tungsten arc (TGA) and electron beam (EB) welding techniques. The gas tungsten arc welds were made under a variety of conditions including using filler metal formed of these alloys, with or without a preheat of 400.degree. C., under normal gas shielding conditions using argon, and in an atmosphere controlled glove box. These TGA welds have also been made with alternating current or direct current and with low and high input welding techniques. The electron beam welds were made on these alloys in a vacuum chamber without preheating. Occasionally, by employing such welding techniques, a crack-free weld was obtained but in most instances the welds were found to contain solidification or hot cracks in the weld fusion zone. Also, when attempts to duplicate a successful crack-free weld were made, hot cracking generally occurred in the weld. This lack of satisfactory weldability found in these nickel aluminide alloys represents a significant drawback to the use of these otherwise desirable alloys in many engineering applications.